A survey of seismic activity near wairakei geothermal field, New Zealand

Abstract

A five-week survey showed that seismic activity within 20 km of Wairakei Geothermal Field took place mainly at shallow depths (< 2 km), in or close to the Taupo Fault Belt, and occurred in swarms. Twenty-eight earthquakes, with magnitudes (M) between -1.3 and +2.8, were located; 43 other earthquakes, with M < 0.2, were recorded but could not be located. The distribution of located earthquakes did not correlate with known areas of surface geothermal activity. No located earthquake occurred beneath the main production borefield or an area of ground subsidence adjacent to the borefield. A value for b of 0.7 ± 0.2 was obtained for events with −0.8 < M ⩽ + 1.25 within 6.5 km of the borefield. No earthquakes were sufficiently clearly recorded to demonstrate attenuation of S-phases within the borefield area. Seismic activity in and near the field is similar to that reported in neighbouring parts of the region; operation of the field, therefore, does not appear to have caused any large increase or decrease of seismic activity in the Taupo Fault Belt within or near the field.